Granular material in bulk form, such as sugar, grains and the like, often are stored in stationary silos and transported in specially designed bulk freight vehicles. Such storage and transport containers often have rigid walls and bottoms made of metal or some other rigid material. A discharge port generally is provided in the bottom of such a container, which, when opened, permits the material in the container to flow out. From the discharge port, the material may be conveyed by any suitable conveying means. If the bottom of the container, extending from the discharge port to the walls, is flat or horizontal, not all of the granular material will be discharged through the discharge port by gravity. It is a characteristic of granular material contained in a flat-bottomed container to stop flowing out of a discharge port when the material remaining in the container is at an angle of repose. The material remaining in the container after discharge by gravity often forms a cone shape inside the container. The inner face of this cone shape, formed by the granular material, extends from the discharge port in the bottom of the container upward at an angle to the wall of the container. The angle of repose at which this cone shape occurs and discharge by gravity ends depends on the physical characteristics of the bulk material involved.
To facilitate the discharge of the entire content of a bulk storage container, silos and bulk freight vehicles often are provided with hopper bottoms. Such hopper bottoms are generally cone-shaped, extending upwardly from the discharge port at an angle towards the bulk container walls. The angle at which the hopper bottom projects from the discharge port to the walls of the storage container is intended to be sufficient to prevent the material in the bin from resting in a cone shape at an angle of repose and to avoid bridging, rat-holing and the like of the material so that the entire contents of the storage container is directed towards the discharge port for removal. A storage container with a hopper bottom has a higher center of gravity than the same sized bin with a flat bottom. This higher center of gravity may not be a significant problem in stationary silos, but may be of greater importance in a mobile bulk freight vehicle. Moreover, a hopper-shaped storage container is expensive and wasteful of space.
It is highly desirable to have a cargo space of a freight vehicle that would be suitable for handling either bulk goods or piece goods such as palletized packages and the like. The obvious advantage is that the same cargo space on the same vehicle could handle either of these two significantly different types of loads. Convertibility of cargo space provides extreme flexibility and avoids empty runs of the vehicle. For example, a truck-trailer could handle piece goods such as palletized bags of sugar on one run and on a return run could handle bulk goods such as sugar in the bulk going back to the packaging factory; a plastics company could send finished goods in standard cargo space and return with a bulk load of resins; a brewer could send kegs or cases of beer and bring back malt or grains in the same vehicle, and there are many other uses of a similar nature.
The economic advantages of convertible freight vehicles have sparked an increased interest therein in recent years. For example, a van sold by Converta-Vans, Inc. of Wescoville, Pennsylvania, provides a cargo space with four separate convertible bulk hoppers covered by hinged floor sections in the piece goods mode, the hinged floor sections being raisable to provide wall sections that slope towards the hoppers in the bulk mode for gravity discharge of bulk materials through the hoppers. These hoppers make the van expensive and heavy, and the weight contributes to the energy expenditure of hauling. Also, the hinged floor sections that form sloping walls in the bulk mode raise the center of gravity of the load. Moreover, general cargo vans are not easily converted to the Converta-Van configuration due to the necessity of providing the hoppers.
Other hopper-type freight vehicles that are convertible from a bulk-handling mode to a piece goods handling mode are shown in U.S. Pat. Nos. 3,738,511; 3,756,469; 4,092,051; 4,155,469 and 4,606,570.
One proposal for a convertible freight vehicle that avoids the necessity of hoppers is shown in U.S. Pat. No. 2,712,797 to Woehrle et al. In Woehrle, a cargo space for piece goods in a van-type body is converted to a cargo space suitable for the transportation of bulk good by providing a liner for the cargo space with a rear discharge spout. For discharge of bulk materials, the van-type body of the freight vehicle is tiltable in the manner of a dump truck. However, a tilting mechanism that tilts an entire loaded van-type body would necessarily be quite expensive and add considerable undesired weight to the vehicle.
A freight vehicle with a convertible cargo space that requires neither a hopper bottom nor a dump truck-like tilting mechanism is shown in U.S. Pat. No. 4,534,596 to Timothy C. Bonerb, the inventor of the present invention. The freight vehicle disclosed in U.S. Pat. No. 4,534,596 modifies a conventional cargo space for piece goods by providing openings in the roof and floor for filling and discharging bulk material. One or more double-walled inflatable bags having their bottoms attached to rigid support platforms are positioned in erected condition to handle bulk material and are movable to a stored position near the roof of the cargo space to allow handling of piece goods.
Other bulk unloading systems that do not require fixed hoppers are shown in U.S. Pat. Nos. 4,541,765 to Moore and 2,829,803 to Paton. The Moore apparatus includes a collapsible rectangular liner having a collapsible funnel-shaped base wherein after partial discharge, the collapsible liner is raised to extend the collapsible funnel-shaped base above the angle of repose of the bulk material and thereby complete discharge of the bulk material. The Paton system employs a flat bottom and flexible walls, and means for changing the relative pressure between air within the container and are on the outer surface of the flexible walls of the container. This change in relative air pressure causes inward movement of the flexible walls which raises the flat bottom portion thereby sloping the flat bottom portion to complete discharge of the bulk material.
Other dump-type systems are known in the art. For example, a mechanically actuated dump system for emptying a freight vehicle through a fixed hopper is shown in U.S. Pat. No. 612,053. Dump systems showing inflatable tilting means are shown in U.S. Pat. Nos. 3,659,899; 3,711,157; 3,784,255 and 4,572,579.
There remains a need in the art for improvements in bulk storage bins.